Luminescent materials, termed phosphors, have general utility in a broad range of lighting and display applications. A phenomenon common to all such applications is excitation of the phosphors in accordance with any one of a number of excitation techniques known in the art, causing the phosphors to emit light. Known excitation techniques include exposing the phosphors to various external energy sources. The excitation means can be electrons, ultra violet, x-rays, or gamma rays, to name a few. This excitation phenomenon is apparent in virtually all types of conventional, phosphor-containing, host lighting or display fixtures. Among such conventional fixtures are fluorescent tubes, cathode ray tubes, gas discharge plasma displays, vacuum fluorescent displays, and field emission displays.
Cathode ray tubes are typical of luminescent displays employing electrons as the excitation means for the phosphors. Such displays have a display screen including an anode panel coated with phosphors that are selectively excited by electrons directed toward the phosphors from an adjacent electron-supplying cathode. The excited phosphors emit light, thereby creating a desired image visible to the viewer on the display screen. Phosphors having utility for display applications typically comprise a host lattice impregnated with a quantity of a dopant that activates luminescent properties in the resulting composition. The phosphors are conventionally manufactured by selecting the host lattice and dopant from preselected materials, mixing the materials, heating the mixed materials in the presence of a flux to effectuate infiltration of the dopant into the host lattice, and washing the fired material to remove the flux and obtain the desired phosphor for use in a host lighting or display fixture.
Many host lighting and display fixtures have performance requirements related to their particular area of application that define a need for specialized phosphors possessing performance characteristics satisfying these performance requirements. For example, in radar applications, it is desirable that pixels of transient luminescence visually persist on the radar display screen for many seconds after initial appearance thereof. Consequently, radar applications require phosphors having the specific performance characteristic of a slow rate of luminescent decay producing a relatively long afterglow. Although phosphors exhibiting a long afterglow are presently known, such phosphors typically have a short lifetime, diminishing their utility. By way of further example, it is desirable in certain other applications to operate the displays at a very low voltage, while providing a relatively bright display for clear visibility even in daylight. Such applications require phosphors having the specific performance characteristic of bright luminescence upon low-voltage excitation. In sum, it is apparent that an overall need exists for the manufacture of specialized phosphors capable of meeting the performance requirements of certain host lighting and display fixtures.
Accordingly, it is an object of the present invention to provide a process for manufacturing phosphor products satisfying predetermined performance requirements for specialized applications. More particularly, it is an object of the present invention to provide a process for manufacturing a phosphor product having long afterglow characteristics. It is another object of the present invention to provide a process for manufacturing a phosphor product having bright luminescent characteristics upon low-voltage excitation. It is a further object of the present invention to provide a phosphor product having long afterglow characteristics for specialized display applications such as radar screens. It is yet another object of the present invention to provide a phosphor product having bright luminescent characteristics upon low-voltage excitation for alternate specialized display applications. It is still another object of the present invention to provide a luminescent display device employing a phosphor product having bright luminescent characteristics upon low-voltage excitation. It is still a further object of the present invention to provide a luminescent display device employing a phosphor product having long afterglow characteristics. These objects and others are accomplished in accordance with the invention described hereafter.